We have developed techniques for the isolation of condensed DNA and condensed chromatin from bacterial cells and interphase eukaryotic cells, respectively. Physical-chemical studies of th bacteral DNA have demonstrated that the DNA is packaged in a structure closely resembling the bacterial nucleoid. This research is intended to elucidate certain general features of the conformational organization of DNA as it is packaged in the cell. Methods, utlizing DNA intercalating dyes, are now available for quanitating the amount of supercoiling in the packed DNA; and we have developed sedimentation methods for estimating the degree of DNA folding in the particls. Using these methods combined with certain other techniques which permit both controlled unfolding and controlled relaxation of supercoiling in the packaged DNA we propose the following research objectives: 1) to determine the molecular interactions which organize folds in the condensed DNA of chromosomes, 2) to define interactions in chromosomes which segregate the DNA into regions of independent supercoiling, 3) to determine if the orgabized conformation of condensed bacterial DNA is a static or dynamic structure, 4) to begin investigations of the state of supercoiling and folding of condensed chromatin isolated from interphase eukaryotic cells (Neurospora crassa and Chinese hamster).